PI-controlled bioreactor as a generalized Lienard system

It is shown that periodic orbits can occur in Cholette's bioreactor model working under the influence of a PI-controller. We find a diffeomorphic coordinate transformation that turns this controlled enzymatic reaction system into a generalized Lienard form. Furthermore, we give sufficient conditions for the existence and uniqueness of limit cycles in the new coordinates. We also perform numerical simulations illustrating the possibility of the existence of a local center (period annulus). A result with possible practical applications is that the oscillation frequency is a function of the integral control gain parameterComment: 15 pages, 5 figures, accepted version at Computers & Chem. En

Alien Fishes In Lakes Of The Doce River Basin (brazil): Range, New Occurrences And Conservation Of Native Communities

The present study shows the distribution of alien fish species in tropical lakes in the middle Doce river basin, southeastern Brazil, obtained from a rapid assessment program. The causes for their introductions were sport-fishing improvement in some specific lakes and aquaculture in the studied basin. Presently, these species have a wide distribution occurring in 41 of the 54 lakes studied, representing an actual threat to regional native fish community. The natural connection among lakes and streams during the rainy season and the dispersal mediated by local people are the main invasion agents for alien fishes. The success of these invaders is probably due to absence of pre-existing effective competitors or top-predators in the invaded communities. We consider that the eradication of alien fishes by means of the available management tools may be very difficult due to the large number of lakes invaded and to the wide spectrum of lake conditions and resources exploited by these alien species. We recommend the use of environmental education as a tool to stop the human-mediated dispersion of aliens and to improve conservation of native fish community in lakes where these alien species are not present yet. © 2004 Instituto de Ciências Biológicas - UFMG.52135142Agostinho, A.A., Júlio, H.F., Ameaça ecológica: Peixes de outras águas (1996) Ciência Hoje, 21, pp. 36-44Arthington, A.H., Mitchell, D.S., Aquatic invading species (1986) Ecology of Biological Invasions, pp. 34-53. , Groves, R. H. & Burdon, J. J. (Ed.) Melbourne, Cambridge University PressFerber, D., Will Black Carp Be the Next Zebra Mussel? 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Belo Horizonte, Fundação BiodiversitasGuan, R., Wiles, P.R., Ecological Impact of Introduced Crayfish on Benthic Fishes in a British Lowland River (1997) Conservation Biology, 11, pp. 641-647Hall, S.R., Mills, E.L., Exotic species in large lakes of the world (2000) Aquatic Ecosystem Health and Management, 3, pp. 105-135Howard, G.H., Control Options: Fresh-water Invasives (2000) "Best Management Practices for Preventing and Controlling Invasive Alien Species", pp. 1-8. , Paper presented to the Workshop on Cape Town, South AfricaHuckins, C.J.F., Osenberg, C.W., Ittelbach, G.G., Species introductions and their ecological consequences: An example with congeneric sunfish (2000) Ecological Applications, 10, pp. 612-625Jackson, D.A., Peres-Neto, P.R., Olden, J.D., What controls who is where in freshwater fish communities - The roles of biotic, abiotic and spatial factors (2001) Canadian Journal of Fisheries and Aquatical Sciences, 58, pp. 157-170Katunzi, E.F.B., Zoutendijk, J., Goldschmidt, T., Wanink, J.H., Lost, W.F., Lost zooplanktivorous cichlid from Lake Victoria reappears with a new trade (2003) Ecology of Freshwater Fish, 12, pp. 237-240Kolar, C.S., Lodge, D.M., Progress in invasion biology: Predicting invaders (2001) Trends in Ecology and Evolution, 16, pp. 199-204Latini, A.O., Estado Atual e Perspectivas para a Ictiofauna da Região do Parque Estadual do Rio Doce, MG (2001) Plano de Manejo Do Parque Estadual Do Rio Doce, pp. 1-49. , Instituto Estadual de Florestas & Projeto Doces Matas (Ed.) Belo Horizonte, MGLatini, A.O., Por que nossos rios têm menos peixes? (2002) Ciência Hoje, 30, pp. 58-59Latini, A.O., Petrere, M., Reduction of a native fish fauna by alien species: An example from Brazilian freshwater tropical lakes (2004) Fisheries Management and Ecology, 11, pp. 71-79Lima, F.P., (2003) E Os Lagos... Como Vão? Percepção Ambiental E O Problema Da Invasão de Espécies Exóticas Na Bacia Do Médio Rio Doce, pp. 1-46. , Trabalho de conclusão do curso de Ciências Bioló gicas. Viçosa, Universidade Federal de ViçosaLowe-Mcconnell, R.H., (1999) Estudos Ecológicos de Comunidades de Peixes Tropicais, p. 535. , São Paulo, Editora da Universidade de São PauloMack, R.N., Simberloff, D., Lonsdale, W.M., Evans, H., Cout, M., Bazzaz, F.A., Biotic Invasions: Causes, Epidemiology, Global Consequences and Control (2000) Ecological Applications, 10, pp. 689-710Marchetti, M.P., Moyle, P.B., Levine, R., Alien fishes in California watersheds: Characteristics of successful and failed invaders (2004) Ecological Applications, 14, pp. 587-596Moyle, P.B., Light, T., Fish Invasions in California: Do Abiotic Factors Determine Success? (1996) Ecology, 77, pp. 1651-1670Myers, N., Mittermeier, R.A., Mittermeier, C.G., Fonseca, G.A.B., Kent, J., Biodiversity hotspots for conservation priorities (2000) Nature, 403, pp. 853-858Olden, J.D., Poff, L.N., Douglas, M.R., Douglas, M.E., Faush, K.D., Ecological and evolutionary consequences of biotic homogenization (2004) Trends in Ecology and Evolution, 19, pp. 18-24Ricciardi, A., Maclssac, H.J., Recent mass invasion of the North American Great Lakes by Ponto-Caspian species (2000) Trends in Ecology and Evolution, 15, pp. 62-65Sakai, A.K., Allendorf, F.W., Holt, J.S., Lodge, D.M., Molofsky, J., With, K.A., Baughman, S., Weller, S.G., The population biology of invasive species (2001) Annual Review in Ecology and Systematics, 32, pp. 302-332Sala, O.E., Chapin Iii, F.S., Armesto, J.J., Berlow, E., Bloomgield, J., Dirzo, R., Huber-Sanwald, E., Wall, D.H., Global Biodiversity Scenarios for the Year 2100 (2000) Science, 287, pp. 1770-1774Simberloff, D., Eradication of island invasives: Pratical actions and results achieved (2001) Trends in Ecology and Evolution, 16, pp. 273-274Thomas, M.H., Randall, A., Intentional introductions of nonindigenous species: A principal-agent model and protocol for revocable decisions (2000) Ecological Economics, 34, pp. 333-345Tundisi, J.G., De Meis, M.R.M., Geomorphology and limnological processes at the Middle Rio Doce Valley (1985) Limnological Studies in Rio Doce Valley Lakes and Pantanal Wetland, pp. 11-17. , Saijo, Y. & Tundisi, J. 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“Astonishing successes” and “bitter disappointment”: The specific heat of hydrogen in quantum theory

The specific heat of hydrogen gas at low temperatures was first measured in 1912 by Arnold Eucken in Walther Nernst’s laboratory in Berlin, and provided one of the earliest experimental supports for the new quantum theory. Even earlier, Nernst had developed a quantum theory of rotating diatomic gas molecules that figured in the discussions at the first Solvay conference in late 1911. Between 1913 and 1925, Albert Einstein, Paul Ehrenfest, Max Planck, Fritz Reiche, and Erwin Schrödinger, among many others, attempted theoretical descriptions of the rotational specific heat of hydrogen, with only limited success. Quantum theory also was central to the study of molecular spectra, where initially it was more successful. Moreover, the two problems interacted in sometimes surprising ways. Not until 1927, following Werner Heisenberg’s discovery of the behavior of indistinguishable particles in modern quantum mechanics, did American theorist David Dennison find a successful theory of the specific heat of hydrogen